The disclosure of Japanese Patent Application No. 2001-124579 filed on Apr. 23, 2001, including the specification, drawing and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a control system for an internal combustion engine, and more particularly to an air intake control system having an intake air flow control valve disposed downstream of a throttle valve.
2. Description of Related Art
Japanese Patent Laid-Open No. 7-83101 or Japanese Patent Laid-Open No. 2000-73843 discloses an air intake control system for an internal combustion engine. In the aforementioned control system, an intake air flow control valve disposed downstream of a throttle valve within an intake air passage is closed upon cold starting for raising the negative pressure in the intake air passage to enhance volatility of the injected fuel using a boiling effect under reduced pressure, and to generate a tumble flow in a cylinder, thus improving a combustion in the cylinder.
Recently further improvement in fail-safe performance has been required, and various arts have been developed to cope with the demand. The aforementioned related arts respectively disclose fail-safe technologies against a failure in the intake air flow control valve, but disclose no fail-safe technologies against a failure in the throttle valve or a damage to an intake system.
The invention thus provides a control system for an internal combustion engine having a fail-safe function against a failure in the throttle valve or damage to the air inlet system.
According to an aspect of the invention, a control system for an internal combustion engine is provided with a throttle valve provided within an intake passage of the internal combustion engine and controlling an intake air quantity, an intake air flow control valve that is provided downstream of the throttle valve within the intake passage, and a controller that controls the intake air flow control valve to be opened and closed in accordance with an operation state of the internal combustion engine. The controller controls an intake air quantity by adjusting an opening amount of the intake air flow control valve when it is determined that the intake air quantity cannot be controlled by the throttle valve.
Unlike the throttle valve, the intake air flow control valve has a vent hole and, therefore, is not expected to have a function of adjusting the intake air quantity. However a rough adjustment of the intake air quantity can be made by adjusting an opening amount of the intake air flow control valve, though such adjustment is not performed as accurately as being performed by the throttle valve. Thus, it is possible to realize a fail-safe function that allows a safe limp-home running by adjusting the intake air quantity using the intake air flow control valve upon an unexpected abnormal state of the engine such as a failure in the throttle valve or the damage to the intake system.
Further, it is preferable that a torque of the internal combustion engine be controlled parallel with the air quantity control. As described above, the intake air flow control valve is not expected to have the function of adjusting the intake air quantity, and the range for adjusting the intake air quantity is thus limited. A fine adjustment of the torque by correcting at least one of the ignition timing, fuel injection amount, and variable valve timing prevents an increase in emissions and allows stable limp-home running.